The present invention relates to a plasma etching apparatus and etching method and, more particularly, to a plasma etching apparatus and etching method suitable for forming a fine pattern in the semiconductor manufacture process.
In the semiconductor manufacture process, the plasma etching apparatus is widely used in the fine processing processes, for example, such as film deposition, etching, and ashing. The process by plasma etching performs the predetermined process by making processing gas introduced into the vacuum chamber (reactor) plasmatic by the plasma generation means, performing the fine processing by making it react on the surface of a semiconductor wafer, and discharging volatile reaction products.
In this plasma etching process, the temperatures of the inner wall of the reactor and wafer and the deposition status of reaction products on the inner wall greatly affect the process. If reaction products deposited inside the reactor are peeled off, dust may be caused, resulting in deterioration of the element characteristics and reduction of the yield.
Therefore, in the plasma etching apparatus, to keep the process stable and control generation of foreign substances, it is important to control the temperature in the reactor and deposition of reaction products on the surface.
For example, in Japanese Patent Application Laid-Open 8-144072, for the purpose of improving the selection ratio in the dry etching process of a silicon oxide film, a dry etching apparatus for controlling and holding the temperature of each unit inside the reactor at a high temperature within a range of 150xc2x0 C. to 300xc2x0 C. (desirably from 200xc2x0 C. to 250xc2x0 C.) which is higher than the temperature at the etching stage of 150xc2x0 C. or more with the accuracy of less than xc2x15xc2x0 C. is described. When the temperature of each unit of the inner surface of the reactor is increased and controlled at a high value by heating like this, the deposited amount of plasma polymeric products on the inner surface of the reactor reduces, and the deposited amount of plasma polymeric products on a semiconductor wafer increases, and the selection improves.
In Japanese Patent Application Laid-Open 5-275385, a parallel plate type plasma etching apparatus in which a heating means for increasing and keeping the temperature so that reaction products generated by the plasma etching will not be deposited is installed on at least one of the clamp ring (workpiece holding means) and focus ring (plasma centralization means) is described. As a heating means, a resistance heating element is used. Deposition of reaction products can be prevented by heating, so that peeling of reaction products and deposition of particles on the surface of a workpiece can be reduced.
As mentioned above, in the plasma etching apparatus, it is important to control the temperature of the surface of the inner wall of the chamber and deposition of reaction products on the surface of the inner wall.
However, when the temperature of the inner wall surface of the chamber, particularly the temperature of the side wall surface having a wide area is set to a high value between 200xc2x0 C. and 250xc2x0 C. or more, the etching characteristic becomes very sensitive to the temperature of the inner wall surface and a problem arises that the reproducibility and reliability of the process are apt to reduce.
For example, in S. C. McNevin, et al., J. vac. Sci. Technol. B 15(2) Mar/Apr 1997, p. 21, Chemical challenge of submicron oxide etching"", it is indicated that when the side wall temperature changes from 200xc2x0 C. to 170xc2x0 C. in inductive coupling plasma, the oxide film etching rate increases more than 5%. As a reason, it is inferred that since the side wall temperature lowers, much more carbon is adsorbed into the wall, and deposition of carbon on a wafer reduces, and the oxide film etching rate increases. As mentioned above, since high density plasma, particularly, performs a strong interaction with the inner wall of the reactor in the high temperature zone, deposition of reaction products on the inner wall surface and composition change of the surface proceed rapidly due to a change in the temperature balance inside the reactor and appear as a change in the etching characteristic.
Furthermore, in the high temperature zone, the aforementioned interaction between the plasma and the inner wall becomes very sensitive to a change in temperature. For example, when SiO2 is used as a material of the inner wall surface, a thermodynamic relationship between the etching rate by F atoms of SiO2 and the wall temperature is reported (D. L. Flamm, et al., J. Appl. Phys., 50, p. 6211 (1979)), and when this relationship is applied to a temperature zone of more than 150xc2x0 C., the etching rate rapidly increases exponentially when the wall temperature is between 200xc2x0 C. and 250xc2x0 C. or more.
Therefore, in such a high temperature zone, the temperature control requires high accuracy such as xc2x15xc2x0 C. max. However, the inner wall surface is exposed to high density plasma, so that it is not easy to control the wall surface temperature with high accuracy in such a high temperature zone. To realize it, a temperature detection means and a heating means such as a heater and lamp are used for temperature control, though the temperature control mechanism and means are largely scaled. Furthermore, in such a high temperature zone, reaction products are not deposited on the inner wall surface, so that the wall surface is etched and consumed by plasma. Therefore, it is necessary to periodically exchange the parts of the inner wall surface and an increase in the cost of expendable supplies results. Heating requires large energy, thus the high temperature zone is not desirable also from a viewpoint of energy consumption.
The same problem is imposed also by heating the ring around a wafer and the electrode. When the ring is heated to increase the temperature thereof, deposition of reaction products can be prevented, though the heating mechanism such as the resistance heating element makes the equipment constitution complex. When the ring and inner wall surface are etched and consumed by plasma even if deposition of reaction products can be prevented, there is the possibility that the constitution material itself will become a new dust source. Furthermore, when the parts of the ring and inner wall surface are consumed, it is necessary to periodically exchange them and the running cost of the equipment increases.
One method for solving such a problem is to protect the inner wall surface of the chamber by a surface coating layer of a polymer. For example, in Japanese Patent Application Laid-Open 7-312363, a plasma etching apparatus for keeping the temperature of the workpiece (article to be processed) holder higher than that of the wall surface of the chamber and forming a surface coating layer on the inner wall surface of the chamber is described. By catching and storing contaminant particles in a polymer film, remaining and storing of contaminants in the chamber due to reaction products can be reduced.
However, the purpose in this case is not to protect the wall surface but to catch contaminant particles. It is just described that the temperature for forming a surface coating layer on the inner wall surface of the chamber is lower than that of a workpiece (article to be processed) by more than 5xc2x0 C. and the temperature range and control accuracy are not taken into account. The pressure range is a high pressure range such as several hundreds mtorr (several tens Pa). However, it is inferred that the deposition temperature of a film changes the composition and quality of the film and affects the film peeling strength and occurrence of foreign substances. It is expected that changing of the deposited film temperature results in occurrence of cracking and peeling due to repetition of thermal expansion and shrink and causes foreign substances and the temperature control accuracy is an important factor. Within a pressure range of several tens mtorr max. (several Pa max.), it is considered that the film deposition condition varies due to high ion energy and a longer mean free distance of molecules, Furthermore, in the aforementioned prior art, it is necessary to remove the coating layer catching contaminants from the wall surface of the plasma etching chamber and it directly affects the throughput of the equipment and the cost of expendable supplies. However, this respect is not taken into account.
The present invention is designed to eliminate the difficulties mentioned above and an object of the present invention is to provide a plasma etching apparatus maintaining the reproducibility and reliability of the process at a low cost for a long period of time so as to prevent the etching characteristic from a change with time by controlling the inner temperature of the reactor and deposition of reaction products.
The inventors have given diligent study to the aforementioned problems and as a result of it, found that when the inner wall surface temperature in the reactor is controlled to a temperature sufficiently lower than that of a wafer and a constant temperature within a pressure range of several Pa max. in the reactor, a strong coating film is formed on the inner wall surface. As a result of more detailed analysis, the inventors have acknowledged that this coating film is polymerized much more when the temperature at film forming time is lower, and when the temperature at film forming time is controlled constant, a solid layer structure is formed, accordingly the film surface is not peeled off and damaged and dust is not caused.
In the above description, that the inner wall surface temperature in the reactor is xe2x80x9csufficiently lower than that of a wafer and constantxe2x80x9d means that the temperature is controlled with the accuracy of less than xc2x110xc2x0 C. within a range lower than that of a wafer by 5xc2x0 C. or more, desirably within a range lower by 20xc2x0 C. or more. When the temperature of a wafer during processing is almost within a range from 100xc2x0 C. to 110xc2x0 C., it means that the temperature range is 100xc2x0 C. or lower, desirably 80xc2x0 C. or lower.
On the other hand, in the reactor, there is a part or a component part where the control in the aforementioned low temperature zone is difficult. The inventors have given study also to such a part and as a result of it, found a method for controlling the temperature and deposition of reaction products on the surface without using a complicated heating mechanism such as a heating resistor.
The present invention is designed on the basis of the aforementioned acknowledge and provides a plasma etching apparatus comprising a vacuum processing chamber, a plasma generation device, a processing gas supply means for supplying gas to the processing chamber, an electrode for holding a sample to be processed in this vacuum processing chamber, and an evacuation system for reducing the pressure of the vacuum processing chamber, which is characterized in that the processing gas includes at least one kind of gas having a composition for forming a polymerized film by plasma discharge, and the processing gas is made plasmatic by plasma discharge in the processing chamber, and at least one part of the inner wall surface (or the surface of an internal component part) in contact with plasma in the processing chamber is controlled to a constant temperature which is sufficiently lower than that of a sample, and a strong polymerized film is formed on the inner wall surface of the processing chamber.
Another characteristic of the present invention is that the temperature of the inner wall surface for forming the aforementioned polymerized film is controlled with the accuracy of less than xc2x110xc2x0 C. within a range lower than that of the sample by 5xc2x0 C. or more, desirably within a range lower by 20xc2x0 C. or more.
Another characteristic of the present invention is that the processing pressure in the processing chamber is set within a range from 0.1 Pa to 10 Pa, desirably from 0.5 Pa to 4 Pa.
Another characteristic of the present invention is that the member constituting the inner wall surface of the processing chamber for forming the aforementioned polymerized film has a structure that it can be easily exchanged.
Another characteristic of the present invention is that the apparatus includes a process of controlling the growth of the aforementioned polymerized film formed on the inner wall surface of the processing chamber.
Still another characteristic of the present invention is that in the plasma etching apparatus comprising a vacuum processing chamber, a plasma generation device, a processing gas supply means for supplying gas to the processing chamber, an electrode for holding a sample to be processed in this vacuum processing chamber, and an evacuation system for reducing the pressure of the vacuum processing chamber, the component part (or the inner wall surface) in contact with plasma in the processing chamber is structured so that the bias power is applied to at least one part of the component part, and the heat capacity thereof is made sufficiently small, and the surface area thereof is made smaller.
Another characteristic of the present invention is that the temperature of the component part in contact with plasma in the processing chamber is adjusted within a range from 100xc2x0 C. to 250xc2x0 C., desirably from 150xc2x0 C. to 200xc2x0 C. and furthermore, the processing pressure is set within a range from 0.1 Pa to 10 Pa, desirably from 0.5 Pa to 4 Pa.
Another characteristic of the present invention is that the component part of the inner wall is ring-shaped and the surface area of the part in contact with plasma is 20% of the total area of the inner wall of the processing chamber or less.
Another characteristic of the present invention is that the component part in contact with plasma in the processing chamber, in which the bias power is applied to at least one part thereof is ring-shaped, and the thickness thereof is 6 mm or less, and the inner diameter thereof is more than the diameter of a sample
Still another characteristic of the present invention is that the plasma etching apparatus is structured so that an infrared absorber is formed in the neighborhood of the side of the component part of the inner wall which is in contact with plasma and the temperature of the part is remotely controlled by the infrared radiation means.
Another characteristic of the present invention is that the temperature of the part whose temperature is controlled by the aforementioned infrared radiation is controlled with the accuracy of less than xc2x110xc2x0 C. within a range from 100xc2x0 C. to 250xc2x0 C., desirably from 150xc2x0 C. to 200xc2x0 C.
Still another characteristic of the present invention is that in the plasma etching apparatus, the plasma generation apparatus is a magnetic field UHF band electromagnetic wave radiation and discharge system.
According to the present invention, a part of processing gas is polymerized by plasma discharge and a surface coating layer is formed by polymer on the part of the inner wall of the processing chamber which is in contact with plasma or the surface of the part. By controlling the temperature of the inner wall surface of the reactor to a constant temperature sufficiently lower than that of a wafer, the polymerization of the coating layer proceeds and a solid layer structure can be formed. Therefore, the inner wall surface will not be etched and consumed by plasma, so that the frequency of part exchange of the inner wall surface can be reduced and the running cost can be decreased. Even if the coating layer is exposed to plasma, peeling and damage are not caused to the surface thereof because the film composition is dense, so that dust will not be caused.
Since the temperature of the inner wall surface is set in a temperature zone lower than that of a wafer, as compared with a case that the temperature of the inner wall surface is set in a high temperature zone of 200xc2x0 C. or more, the interaction between plasma and the inner wall surface is weak and not sensitive to a change in temperature. As a result, the reproducibility and reliability of the process hardly reduce for a long period of time and the accuracy of temperature control may be, for example, less than xc2x110xc2x0 C. and can be realized comparatively easily without using a complicated mechanism for temperature control.
When a polymerized film exceeding a predetermined value is formed on the inner wall surface, it is necessary to remove this film. When the equipment is exposed to the air, and the component part of the inner wall surface of the processing chamber on which the polymerized film is formed is exchanged, and the equipment is reoperated, and the film is removed by wet cleaning on an ex-situ basis after removal from the chamber instead of plasma cleaning, and the inner wall surface is reproduced, satisfactory results can be produced such that the non-operation time of the equipment is reduced, and the throughput is prevented from reduction, and the cost of expendable supplies can be reduced by reproduction and repetitive use of parts. When a process of controlling the growth of the polymerized film is added to the process, the time up to opening and cleaning of the equipment can be prolonged.
On the other hand, according to still another characteristic of the present invention, with respect to a part or component part for which the temperature control in a temperature zone sufficiently lower than that of a wafer is difficult, when a structure that the bias power is applied to at least one part thereof is installed in the reactor and the heat capacity of the whole part is made sufficiently small, the whole part can be controlled in a high temperature zone without using a complicated mechanism such as a heater and lamp, so that excessive deposition of reaction products is controlled and an occurrence of foreign substances caused by peeling of reaction products can be reduced. When the surface area of the part is made smaller, the effect on the process can be controlled even if the temperature and surface condition are changed. Furthermore, when the magnitude of bias power to be applied to the component part is adjusted and the temperature is set within a range from 100xc2x0 C. to 250xc2x0 C., desirably from 150xc2x0 C. to 200xc2x0 C., as compared with a case that the temperature is set within a high temperature zone of about 250xc2x0 C. or more, the process is not sensitive to a change in temperature, so that there is an advantage that the temperature change of the component part can be made smaller to a level that will not substantially affect the process.
According to still another characteristic of the present invention, the temperature of the component part in contact with plasma in the processing chamber can be controlled more actively with high accuracy in a high temperature zone using infrared radiation and gas heat transfer, so that excessive deposition of reaction products is controlled, and an occurrence of foreign substances caused by peeling of reaction products can be reduced, and the effect on the process also can be controlled by controlling changes in the temperature and surface condition. Furthermore, when the temperature is controlled with the accuracy of less than xc2x110xc2x0 C. within a range from 100xc2x0 C. to 250xc2x0 C., desirably from 150xc2x0 C. to 200xc2x0 C., as compared with a case that the temperature is set within a high temperature zone of about 250xc2x0 C. or more, the process is not sensitive to a change in temperature, so that there is an advantage that the temperature change of the component part can be made smaller to a level that will not substantially affect even a finer process.